1. Field of the Invention
The present invention relates to photosensitive compositions, and more particularly, to compositions which include a cationic transition metal coordination complex and a borate anion. These inventive compositions are capable of absorbing actinic radiation and producing free radicals which can initiate polymerization of a free radical addition polymerizable or crosslinkable monomer.
2 Description of the Prior Art
U.S. Pat. Nos. 4,399,209 and 4,440,846 to The Mead Corporation describe imaging materials and imaging processes in which images are formed through exposure-controlled release of an image-forming agent from a microcapsule containing a photohardenable composition. The photohardenable composition typically includes an ethylenically unsaturated monomer and a photoinitiator material which is capable of absorbing actinic radiation and producing free radicals to initiate free radical polymerization of the ethylenic monomer. To produce an image, the imaging material is image-wise exposed to actinic radiation and the microcapsules are subjected to a uniform rupturing force. Typically the image-forming agent is a colorless color precursor which is image-wise released from the microcapsules to a developer sheet whereupon it reacts with a developer material to form a visible image.
U.S. patent application Ser. No. 339,917, filed Jan. 18, 1982 (corresponding to U.K. Pat. No. 2,113,860), and U.S. Pat. No. 4,576,891 disclose a full color imaging system wherein three sets of microcapsules which are sensitive to different bands of actinic radiation are employed. These microcapsules respectively contain cyan, magenta and yellow color precursors. The absorption characteristics of the three sets of microcapsules in these photosensitive materials must be sufficiently different that the cyan-forming capsules can be differentially hardened at a predetermined wavelength or over a predetermined wavelength band without hardening the magenta or yellowforming capsules and, likewise, sufficiently different that the magenta-forming and yellow-forming capsules can be selectively hardened upon exposure respectively to second and third wavelengths or wavelength bands, without hardening the cyan-forming capsules or hardening the other of the yellow-forming or magenta-forming capsules. Microcapsules having this characteristic (i.e., cyan-, magenta- and yellow-forming capsules which can be selectively hardened by exposure at distinct wavelengths without cross-exposure) are referred to herein as having "distinctly different sensitivities."
U.S. Pat. No. 4,772,541, also assigned to The Mead Corporation disclose photohardenable compositions including visible light-sensitive photoinitiators. The photoinitiators preferably comprise cationic dye-borate anion complexes represented by the formula ##STR1## wherein D.sup.+ is a cationic dye, and R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently selected from the group consisting of alkyl, aryl, alkaryl, allyl, aralkyl, alkenyl, alkynyl, alicyclic and saturated or unsaturated heterocyclic groups. In practice, the cyan, magenta and yellow color-forming microcapsules are respectively sensitive to red (650 nm), green (550 nm) and blue (450 nm) light, and contain photoinitiators which are sensitive to these wavelengths.
Transition metal coordination complexes capable of photoexcitation have been studied in the literature. See, for example, Sutin and Creutz, "Properties and Reactivities of the Luminescent Excited States of Polypyridine Complexes of Ruthenium (II) and Osmium (II)", Inorganic and Organometallic Photochemistry, pp. 1-27, 1978; Flynn and Demas, "Synthesis and Luminescence of the Tris(2,2'-bipyridine) iridium (III) Ion", Journal of the American Chemical Society, Vol. 96, pp. 1959-1960, 1974; Reitz et al., "Interand Intramolecular Excited-State Interactions of Surfactantactive Rhenium (I) Photosensitizers", Journal of the American Chemical Society, Vol. 110, pp. 5051-5058, 1988; Kober et al., "Synthetic Control of Excited States Nonchromophoric Ligand Variations in Polypyridyl Complexes of Osmium (II)", Inorganic Chemistry, Vol. 24, pp. 2755-2763, 1985; Creutz and Sutin, "Electron-Transfer Reactions of Excited States Reductive Quenching of the Tris(2,2'-bipyridine) ruthenium (II) Luminescence", Inorganic Chemistry, Vol 15, pp. 496-499, 1976.